The black sweatshirt sold by the civil libertarian Electronic Frontier Foundation featured a parody of the National Security Agency’s logo, with the traditional key in an eagle’s claws replaced by a collection of AT&T cables, and eavesdropping headphones covering the menacing bird’s ears. Snowden wore it regularly to stay warm in the air-conditioned underground NSA Hawaii Kunia facility known as “the tunnel.”

His coworkers assumed it was meant ironically. And a geek as gifted as Snowden could get away with a few irregularities.

Months after Snowden leaked tens of thousands of the NSA’s most highly classified documents to the media, the former intelligence contractor has stayed out of the limelight, rarely granting interviews or sharing personal details. A 60 Minutes episode Sunday night, meanwhile, aired NSA’s officials descriptions of Snowden as a malicious hacker who cheated on an NSA entrance exam and whose work computers had to be destroyed after his departure for fear he had infected them with malware.

But an NSA staffer who contacted me last month and asked not to be identified — and whose claims we checked with Snowden himself via his ACLU lawyer Ben Wizner — offered me a very different, firsthand portrait of how Snowden was seen by his colleagues in the agency’s Hawaii office: A principled and ultra-competent, if somewhat eccentric employee, and one who earned the access used to pull off his leak by impressing superiors with sheer talent.

The anonymous NSA staffer’s priority in contacting me, in fact, was to refute stories that have surfaced as the NSA and the media attempt to explain how a contractor was able to obtain and leak the tens of thousands of highly classified documents that have become the biggest public disclosure of NSA secrets in history. According to the source, Snowden didn’t dupe coworkers into handing over their passwords, as one report has claimed. Nor did Snowden fabricate SSH keys to gain unauthorized access, he or she says.

Instead, there’s little mystery as to how Snowden gained his access: It was given to him.

“That kid was a genius among geniuses,” says the NSA staffer. “NSA is full of smart people, but anybody who sat in a meeting with Ed will tell you he was in a class of his own…I’ve never seen anything like it.”

When I reached out to the NSA’s public affairs office, a spokesperson declined to comment, citing the agency’s ongoing investigation into Snowden’s leaks.

But over the course of my communications with the NSA staffer, Snowden’s former colleague offered details that shed light on both how Snowden was able to obtain the NSA’s most secret files, as well as the elusive 30-year old’s character:

Before coming to NSA Hawaii, Snowden had impressed NSA officials by developing a backup system that the NSA had widely implemented in its codebreaking operations.

He also frequently reported security vulnerabilities in NSA software. Many of the bugs were never patched.

Snowden had been brought to Hawaii as a cybersecurity expert working for Dell’s services division but due to a problem with the contract was reassigned to become an administrator for the Microsoft intranet management system known as Sharepoint. Impressed with his technical abilities, Snowden’s managers decided that he was the most qualified candidate to build a new web front-end for one of its projects, despite his contractor status. As his coworker tells it, he was given full administrator privileges, with virtually unlimited access to NSA data. “Big mistake in hindsight,” says Snowden’s former colleague. “But if you had a guy who could do things nobody else could, and the only problem was that his badge was green instead of blue, what would you do?”

As further evidence that Snowden didn’t hijack his colleagues’ accounts for his leak, the NSA staffer points to an occasion when Snowden was given a manager’s password so that he could cover for him while he was on vacation. Even then, investigators found no evidence Snowden had misused that staffer’s privileges, and the source says nothing he could have uniquely accessed from the account has shown up in news reports.

Snowden’s superiors were so impressed with his skills that he was at one point offered a position on the elite team of NSA hackers known as Tailored Access Operations. He unexpectedly turned it down and instead joined Booz Allen to work at NSA’s Threat Operation Center.

Another hint of his whistleblower conscience, aside from the telltale hoodie: Snowden kept a copy of the constitution on his desk to cite when arguing against NSA activities he thought might violate it.

The source tells me Snowden also once nearly lost his job standing up for a coworker who was being disciplined by a superior.

Snowden often left small gifts anonymously at colleagues’ desks.

He frequently walked NSA’s halls carrying a Rubik’s cube – the same object he held to identify himself on a Hong Kong street to the journalists who first met with him to publish his leaks.

Snowden’s former colleague says that he or she has slowly come to understand Snowden’s decision to leak the NSA’s files. “I was shocked and betrayed when I first learned the news, but as more time passes I’m inclined to believe he really is trying to do the right thing and it’s not out of character for him. I don’t agree with his methods, but I understand why he did it,” he or she says. “I won’t call him a hero, but he’s sure as hell no traitor.”